Protective device



April 18, 1933.

GRAY 1,903,996

PROTECTIVE DEVICE Filed April 29, 1926 lnvehfar: Eran/r 9 Gray Patented" Apr. 18, 1933 UNITED STATES PATENT OFFICE rm: our, or new 1031:, n. Y, assronoa 'ro wns'rnmr Emc'rarc courm, moonrom'rnn, or new vonx, n. 2., a conronn'rron or new YORK PROTECTIVE DEVICE Application fled Apr-i129,

This invention relates to rotective devices for electrical apparatus an more particularly to protectors operating in an inert gas at low pressure.

Heretofore, it has been the generally .accepted theory with respect to rotectlon devices that a low voltage brea down is the measure of the ability of a discharge tube to protect against rapid voltage surges. However, such tubes have shown ,a lag in breakdown and consequentl the circuits protected by such tubes may e subjected to a peak voltage far above the voltage at whlch breakdown takes place. Such a conditlon lnfll cts detrimental effects on apparatus with WhlCh the protective device is associated and considerably increases maintenance costs. Protective devices must break down without appreciable time lag and carry the full current for a small time interval. Therefore, the important factors in devices of this character are to obtain a rapid breakd0wn at sparking potentials, a quick dlscharge to prevent interference with the operation of associated apparatus, and the prevention of permanent arcs between electrodes.

The object of this invention is to provide a rotective device having increased rapidity of breakdown and quick discharging characteristics.

Another object is the presention of permanent arcs in the main discharge path of the dev1ce.

This invention is an improvement on my Patent No. 1,603,279, issued October 19, 1926, and entitled, Spark arresters. In this patent the protective device comprises a pair of parallel electrodes spaced by a small unobstructed gap and enclosed in a vessel containing an easily ionized gas at a low pressure.

It is known that the incorporation of an electro-positive material in a discharge tube and operatin in an inert gas is beneficial, as disclosed in S. Patent of Fritz Schriiter, No. 1,605,001, issued November 2, 1926, and entitled Vacuum valves with glow discharge. As disclosed in that patent, the electro-positive material is coated on the electrodes or forms an auxiliary electrode, which is located in the main discharge path so that 1926. Serial No. 105,898.

the discharge takes place at a lower voltage and reduces the absorption-of energy by the discharge.

In accordance with a broad aspect of the present invention, an auxiliary electrode contaming or coated with an electro-positive substance is maintained at the same potential as one of the electrodes to increase the rapidity of breakdown by the distribution of the electro-positlve substance over the operating surface of the electrodes.

A feature of the invention is the location of the auxiliary electrode outside the main discharge path to prevent the formation of permanent arcs between the electrodes.

Another feature is the arrangement of the mam electrodes with respect to the auxiliary electrode so that the discharge plays upon the electrodes, so that the auxiliary electrode is at the same potential as the electrode to which it is connected. The auxiliary electrode contains or is coated with an electropositive substance and is mounted outside the main discharge path, preferably by afiixing it to projections'on the cathode so that the discharge from the anode plays upon the electro-positive substance. This structure is enclosed in a vessel containing an inert gas at a low pressure together with a small percentage of a reducing gas or medium, to lower the breakdown potential. A reversible type of discharge device according to this invention, comprises a similar structure in which each main electrode is provided with an auxiliary electrode containing the electro-positive substance, so that either main electrode may function as a cathode when the other electrode is an anode. In

either event only the auxiliary electrode which is at the same potential as the cathode will be activiated by the discharge.

While the discharge device of this invention, in the preferred form, may contain all the features enumerated, it is understood that the invention is not limited to such a combinatiomsince under certain conditions the operating characteristics of a discharge device may be sufiiciently improved by employing only one or more of the various features.

Referring to the drawing, Fig. 1 illustrates a protective device embodying this invention, Fig. 2 is a cross sectional View of Fig. 1 on the line 22, Fig. 3 is a view of the cross section 3-3 of Fig. 1, Fig. 4 shows a modified form of the invention, Fig. 5 is a cross section of Fig. 4 on the line 55 and Fig. 6 illustrates an application of the invention to a relay circuit.

Referring specifically to Fig. 1, the protective device comprises a glass enclosing vessel 1, in which the electrodes 2 and 3, preferably of aluminum, are spaced by a small unobstructed gap and supported by means of leading-in Wires 4 and 5 sealed in the lower end of the glass vessel 1. The electrodes are formed of metal punchings and insulated at either end by mica strips 6 held in position by the prongs 7 on the electrode 3. This arrangement provides an efficient assembly of the electrodes whereby the discharge is confined to a portion of the electrodes substantially removed from the insulating spacers. A filling of an inert gas, such as argon, surrounds the electrodes, together with a reducing gas, such as hydro gen, whereby the active state of the electrodes is increased. This construction is disclosed and claimed in my patent previously mentioned.

While it was found that the use of hydrogen together with the spacing of the electrodes produced rapid operation of the device, it was discovered that the combina-' tion of the inert and reducing gases with certain electro-positive material or an alkali compound greatly increased the rapidity of operation and facilitated the quick discharge of the sparking potential.

The electro-positive material or alkali compound is inserted in the device by combining it with an auxiliary electrode. Preferably the material is coated on an aluminum strip 8, and the coated strip is attached to the electrode 3, which is the cathode, by soldering to the nodal projections 9. This arrangement forms a suitable support for the auxiliary electrode whereby the cathode and auxiliary electrode are maintained at the same potential. The coated auxiliary electrode 8 is located beyond the cathode so that the cathode forms an incomplete shield to the discharge and also to prevent the formation of permanent arcs between the main electrodes. While this arrangement is the most convenient due to the configuration of the electrodes, the auxiliary electrode 8 may be supported in any other suitable manner in which it will be outside of the main dis charge path and positioned so that a portion of the discharge can play. on the electropositive material.

The coating on the auxiliary electrode 8 may consist of an oxide of an electro-positive substance or an alkali metal, preferably potassium oxide. Similar results may also be obtained with sodium, rubidium or caesium oxide. WVhile it is preferable to use the oxide of these substances in combination with the argon-hydrogen gas mixture, other compounds of the alkaline earth group have been found to be equally efiicient. For instance,

the borates, carbonates and several other compounds of alkali metals may be used to produce an active coating on the auxiliary electrode attached to the cathode, to obtain rapid operation of the discharge device. Furthermore, if a suitable alkali compound is present, the hydrogen may be replaced by nitrogen, helium, acetylene, carbon-dioxide, carbon-monoxide or other reducing gases. Similarly, if magnesium, carbon or a hydrocarbon is combined with the potassium oxide, no reducing gas need be added to the inert gas. Protective tubes containing any of the above combinations have very low voltage breakdown characteristics. For instance, protective tubes in which the strip is coated with a compound of potassium and carbon, break down with an applied potential difference of from 60 to 70 volts.

The anode 2 is preferably made wider than the cathode 3 as shown in Fig. 2 so that the minute particles emitted from the active coat ing on the auxiliary electrode 8 will strike the projecting edge of the anode 2 to distribute the active material over the operating surfaces of the electrodes and combine with the discharge to increase the rapidity of breakdown.

The invention is also disclosed in a reversible typeof protector as shown in Fig. 4, in which the electrodes 2 and 3 are staggered, as shown in Fig. 5 to provide a projecting edge on the electrode acting as anode upon which the particles of the coating may impinge. These electrodes are preferably of similar configuration and each carries a coated auxiliary electrode 8 so that the device may be inserted in a circuit regardless of the polarity of the circuit. As shown in Fig. 6 the protective device is connected in a relaycircuit across the relay contacts 10 and 11 of relay 12. The relay contacts are included in a circuit containing inductance 13 and battery 14. In connecting the protective device as shown in Fig. 1, caution must be exercised to connect the cathode 3 to the negative side of the line and the anode 2 to the positive side. However, with the device shown in Fig. 4 the connections may be made regardless of the polarity of the circuit, since either electrode can function as the cathode while the other electrode functions as the anode. In either case, only the coated auxiliary electrode attached to the cathode is operative.

Obvious changes in the material and construction described above, will occur to those skilled in the art and it is therefore understood that the invention is not limited to any specific construction. Furthermore, the invention is not limited to the protection of relay contacts since it is applicable to the protection of other apparatus in which a rapid voltage breakdown is necessary.

What is claimed is:

1. A protective device comprising an enclosin vessel, a pair of electrodes at least one of which has loops near the ends thereof, said electrodes being separated by a small unobstructed gap and supported in said vessel, a filling of inert gas therein, and an auxiliary member in direct contact with the loops on one of said electrodes, said member containing an oxide of an alkali metal.

2. A protective device comprising an enclosing vessel, a pair of electrodes having a small unobstructed gap therebetween and supported in said vessel, a filling of inert gas therein, and an. auxiliary member in direct contact with the exterior surface and parallel with one of said. electrodes, said member being coated with potassium oxide.

3. A protective device comprising an enclosing vessel, a cathode and anode supported in said vessel and having a small unobeach of said electrodes, said auxiliary electrode being coated with electro-positive material.

6. A protective device comprising an enclosing vessel, a pair of parallel similar electrodes supported in said vessel and spaced by a small unobstructed gap, a filling of inert gas therein, each of said electrodes having an edge projecting beyond the edge of the opposed electrode, and an auxiliary electrode spaced from each electrode and beyond the unobstructed gap between the parallel electrodes, said auxiliary electrode being coated with electro-positive material.

In witness whereof, I hereunto subscribe my name this 26th day of A ril A. D., 1926.

FR K GRAY.

structed ap therebetween, a filling of inert gas therem, an auxiliary electrode located adjacent to and supported by said cathode, and a coating of electro-positive material on said auxiliary electrode, said cathode forming an incomplete shield to the discharge between said anode and said auxiliary electrode.

4. A protective device comprising an enclosing vessel, a pair of main electrodes having a small unobstructed gap therebetween and supported in said vessel, a filling of inert gas therein, an auxiliary electrode adjacent to and supported by one of said main electrodes, the other main electrode having a longitudinal edge projecting beyond the edge of the first mentioned main electrode, and a coating of electro-positive material on said auxiliary electrode.

5. A protective device comprising an en closing vessel, a pair of electrodes supported in said vessel and having a small unobstructed gap therebetween, a filling of inert gas therein, said electrodes being supported in staggered relation, and an auxiliary electrode adjacent to the exterior surface of 

